Scientists have warned that the majority of life of Earth will be wiped out within one billion years due to a steep plunge in atmospheric oxygen levels.
Researchers from Japan and the US modelled how Earth’s atmosphere will change on account of various biological, climatic and geological processes.
An increasing energy flow from a brightening sun, which will raise surface temperatures and reduce photosynthesis, will lead to deoxygenation.
As per the research paper, which was published in Nature Geoscience, it was discovered that deoxygenation in some one billion years will result in the atmosphere returning to an inhospitable, methane-rich composition, similar to the conditions of early Earth.
It’s believed this outcome will occur prior to the arrival of so-called moist greenhouse conditions, during which water will leak from Earth’s atmosphere.
These findings suggest that atmospheric oxygen is not permanently available on habitable planets, with implications for the search for extra-terrestrial life.
Before 2.4 billion years ago, it’s understood planet Earth’s atmosphere had been rich in methane, ammonia, water vapour and neon. However, it didn’t have free oxygen, which was introduced during the ‘Great Oxygenation Event’.
During this event, cyanobacteria living in the Earth’s oceans began producing substantial amounts of oxygen through photosynthesis, causing radical changes in the atmosphere.
This influx of oxygen is credited with having paved the way to support multicellular life, however this also led to the mass extinction of many anaerobic bacteria.
These new findings suggest that, the atmosphere could one day reverse these changes, potentially giving Earth back to anaerobic microorganisms.
The research team wrote:
We find that future deoxygenation is an inevitable consequence of increasing solar fluxes. Its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean–atmosphere–crust system.
Our results suggest that the planetary carbonate–silicate cycle will tend to lead to terminally CO2-limited biospheres and rapid atmospheric deoxygenation.
The oxygenation of Earth’s atmosphere is typically regarded as indicative of the planet’s present biosphere, plants and photosynthetic activity. The logical conclusion of this is that we should search for similar oxygenated worlds when looking for extra-terrestrial life.
However, these findings suggest that, from the perspective of a hypothetical alien observing our planet from a distance, the detection of atmospheric oxygen may only be possible for an approximate two–three tenths of Earth’s lifetime.
If this is also true for other planets, the research team has argued that we might need to adjust our search for life on other worlds to include additional biosignatures, which indicate the potential for life to persist beyond a planet’s oxygen-rich period.
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